The Marriott hotel chain has reported a data breach affecting the personal details of up to half a million of its guests.

The US company has determined there has been unauthorised access to the database of its Starwood branch.

media_cameraMarriott International said that up to 500 million hotel guests may have had their data compromised in a hack of the Starwood Reservation database. Picture: AFP

The discovery came as part of an investigation earlier this month, which had been looking at a cyber attack dating back to 2014, a statement on Friday said.

The company believes the breach affected “up to approximately 500 million guests who made a reservation at a Starwood property”, although some of the records could belong to people who had multiple stays.

media_cameraCEO of Marriott International, Arne Sorenson, has apologised saying: “We fell short of what our guests deserve and what we expect of ourselves.” Picture: AFP

For around 327 million of those reservations, data exposed includes some combination of name, address, phone number, email, passport number, and other personal details, as well as details of the person’s stay, the statement said.

media_cameraThe logo for the W Hotel, owned by Starwood Hotels & Resorts Worldwide, is seen in New York’s Times Square. Picture: AP

Credit card numbers and expiration dates of some guests may have been taken.

“We fell short of what our guests deserve and what we expect of ourselves,” chief executive Arne Sorenson said in a statement.

“We are doing everything we can to support our guests, and using lessons learned to be better moving forward.”

Marriott first became suspicious of a possible hack in September. The Starwood chain of hotels includes Westin, Sheraton, Le Meridien, St Regis and W Hotels.